Solar tower power generation plants rely on concentrated sunlight to generate power. The concentrated sunlight generally results from a field of heliostat mirrors that reflect sunlight at a focal area on the solar power tower, creating an area of concentrated solar energy, which may then be converted into electrical energy through a photovoltaic cell, by heating water to create steam that drives a turbine, and/or any other suitable method. The concentrated solar energy may also be stored in a thermal mass and converted at a later time. The field of heliostat mirrors often includes several hundred to over a thousand heliostat mirrors that track the sun and reflect sunlight towards the focal area of the solar power tower. Because the solar tower power generation plants rely so heavily on the concentration of solar energy, the efficiency of a solar tower power generation plant is heavily affected if the heliostats are inaccurate at tracking the sun and consequently are misaligned away from the focal area of the solar power tower. Heliostats typically track the sun in an open-loop manner, where the known positions of the sun are programmed into each heliostat and the mirror is moved according to the known positions. However, due to inaccuracies that may exist in the known positions of the sun and/or the movements of the heliostat mechanism, the actual orientation of the reflective mirror of the heliostat may not be at the desired location and the reflected sunlight may not be aligned correctly towards the focal area of the solar power tower, which decreases efficiency. According to a report published by Sandia National Laboratories, a reduction in sun tracking errors from just two to one milliradian may reduce the cost of a solar tower power generation plant as much as 5%.
Closed loop systems that track the actual reflection direction of the heliostat and then correct misalignment have been proposed, but are very costly to implement. Examples of such systems are disclosed in U.S. Pat. No. 7,207,327 and U.S. Patent Application Number 2009/0249787 that utilize image recognition techniques located at each heliostat. According to the report published by Sandia National Laboratories, the cost of heliostats constitute about 60% of a solar tower power generation plant. The cost of implementing a reflection direction detection system for each individual heliostat will increase the overall cost of the solar tower power generation plant at least proportionally to the number heliostats in the heliostat field, and with such high numbers of heliostats in each heliostat field, this may substantially increase the cost of the solar tower power generation plant. Cost of solar tower power generation plants is also a significant barrier to wider implementation of solar tower power generation plants.
Thus, there is a need in the solar power tower field to create an improved heliostat alignment system and method that is effective and cost efficient. This invention provides such an improved heliostat alignment system and method.